Police are investigating the theft of 3,000 photographs including images of the Duchess of Cambridge and her children, Prince George and Princess Charlotte, after hackers broke into Pippa Middleton’s iCloud account.

The pictures belonging to Kate Middleton’s sister were offered on WhatsApp to reporters at both the Daily Mail and the Sun by an anonymous seller.

The images included some of the royal children as well as wedding dresses and parties. The Sun said it had been approached by someone using a pseudonym and asking for £50,000 within 48 hours.

Specialist officers at Scotland Yard were investigating after receiving a report of the hackon Friday night. A Met spokesman said: “No arrests have been made. Inquiries are ongoing.”

The Sun quoted a spokesman for Pippa Middleton as saying: “Thank you very much for drawing this to the family’s attention. I can confirm that not only have the lawyers been informed but the police are about to be involved as well.”

The alleged theft comes two years after a host of celebrities, including the Hollywood star Jennifer Lawrence, fell victim to a hacker attack on iCloud, which stores private photos from Apple smartphones and computers. Stolen images were subsequently posted online.

In July it was announced that Pippa Middleton, 33, would marry her financier boyfriend, James Matthews, 40, in 2017. Prince William and Kate said the pair, who had dated for less than a year when the engagement was announced, were a “wonderful couple”.

Matthews is the chief executive of Eden Rock Capital Management Group and the older brother of Spencer Matthew, from the E4 reality show Made in Chelsea. The hedge fund is named after a luxury resort his parents own in the Caribbean.